Thermal Engineering Questions and Answers – Brayton Cycle

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This set of Thermal Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Brayton Cycle”.

1. Gas turbine works on _____
a) Dual cycle
b) Otto cycle
c) Brayton cycle
d) Diesel cycle

Explanation: Brayton cycle is used in gas power plant. It is used in open system that is gas turbine.

2. The compression ratio (r) of dual cycle is equal to _________
a) r = volume of the cylinder at the beginning of the compression/volume of the cylinder at the end of the compression
b) r = volume of the cylinder at the end of the compression/ volume of the cylinder at the beginning of the compression
c) r = clearance volume/ volume of the cylinder at the beginning of the compression
d) r = volume of the cylinder at the end of the compression/clearance volume

Explanation: compression ratio of dual cycle (r)=$$\frac{swept \, volume+clearance \, volume}{clearance \, volume}$$
r=volume of the cylinder at the beginning of the compression/volume of the cylinder at the end of the compression

3. For same maximum pressure and heat input, most efficient cycle is _________
a) Dual cycle
b) Rankine cycle
c) Brayton cycle
d) Diesel cycle

Explanation: Efficiency of brayton cycle is directly proportional to pressure ratio. Therefore for maximum pressure and heat input brayton cycle is most efficient.

4. Which of the following methods cannot be used to increase the efficiency of brayton cycle?
a) Decreasing pressure ratio
b) Increasing pressure ratio
c) Regeneration
d) Heat exchanger

Explanation: Heat exchanger and regeneration is used to increase the efficiency of brayton cycle. Also, efficiency of brayton cycle is directly proportional to pressure ratio.

5. In a brayton cycle heat addition takes place __________
a) At constant volume process
b) At constant pressure process
c) First at constant volume then at constant pressure process
d) First at constant pressure then at constant volume process

Explanation: The sequence of processes in brayton cycle is isentropic compression, isobaric heat addition, isentropic expansion and isobaric heat rejection. Therefore heat addition takes place at constant pressure process

6. In a brayton cycle heat rejection takes place ____
a) At constant volume process
b) At constant pressure process
c) First at constant volume then at constant pressure process
d) First at constant pressure then at constant volume process

Explanation: The sequence of processes in brayton cycle is isentropic compression, isobaric heat addition, isentropic expansion and isobaric heat rejection. Therefore heat rejection takes place at constant pressure process.

7. In brayton cycle regenerator is placed between __________
a) Turbine and heat exchanger
b) Turbine and intercooler
c) Compressor and intercooler
d) Compressor and heat exchanger

Explanation: In regenerative brayton cycle a regenerator is placed between compressor and heat exchanger. The exhaust from turbine before entering in heat exchanger and then compressed in compressor.

8. Reheating will _______ the efficiency of brayton cycle.
a) Decreases
b) Increases
c) Zero
d) Remain same

Explanation: Reheating increases the net work output. Reheating necessarily decreases the efficiency.

9. If regeneration is also used along with reheating the efficiency will _____
a) Decreases
b) Increases
c) Zero
d) Remain same

Explanation: Regeneration in the brayton cycle increases efficiency by recovery of waste heat. Hence if regeneration is also used along with reheating the efficiency will increase.

10. What is the effect of regeneration in brayton cycle work output?
a) Work output increases
b) Work output decreases
c) Work output becomes zero
d) Work output doesn’t change

Explanation: Regeneration in the brayton cycle increases efficiency by recovery of waste heat. It doesn’t change the net work output.

11. In how many stages the compression process is divided in intercooling?
a) One
b) Two
c) Three
d) Five

Explanation: In intercooling the compression process is divided into two stages. Air is compressed in first stage is cooled then further compressed in second stage.

12. Reheat and regeneration in combination used to increases ________
a) Net work output
b) Efficiency
c) Both net work output and efficiency
d) Doesn’t change net work output and efficiency

Explanation: Reheating increases the net work output. Reheating necessarily decreases the efficiency. Regeneration in the brayton cycle increases efficiency by recovery of waste heat. It doesn’t change the net work output.

13. Intercooling and regeneration in combination used to increases _________
a) Net work output
b) Efficiency
c) Doesn’t change net work output and efficiency
d) Both net work output and efficiency